<p>The Central Andes are characterized by a steep climatic and environmental gradient with large spatial and temporal variations of associated hydrological parameters. In this region, important hydrological components are integrated water vapor (IWV) and soil moisture. Both parameters can be monitored in parallel by using Global Navigation Satellite System - Reflectometry (GNSS-R) techniques. Soil moisture can furthermore be estimated using Synthetic Aperture Radar (SAR) data.</p><p>As part of International Research Training Group-StRATEGy project, our research aims at monitoring IWV and soil moisture with new station data in the Central Andes. According to the needs of the research, four independent GNSS ground stations and in-situ soil-moisture sensors were installed in spring 2019. Each station is located at different altitude along the climatic gradient and contains various quality GNSS receivers. It has been shown that high-quality receivers provide precise measurements, while low-quality receivers have not been widely tested for these applications. A goal of this project is the direct comparison of data quality from each site and receiver type. Additionally, soil moisture sensors were installed at each site. This set-up will help to evaluate the quality of the GNSS receivers. Moreover, the GNSS-based remote sensing approaches are directly compared to traditional Time-Domain Reflectometry (TDR) techniques. Meteorological data are used for studying the relation between the magnitude of precipitation events and soil moisture, as well as the time needed to spot a significant change in soil moisture after a precipitation event.</p><p>GNSS-R soil moisture estimations and in-situ measurements were compared with estimations derived from SAR data. More specifically, we used data from Sentinel-1 and Satélite Argentino de Observación COn Microondas (SAOCOM) missions. Sentinel-1 is a fully operational mission that uses C-band wavelengths, while SAOCOM relies on L-band wavelength, but is still in a calibration phase. We analyze both wavelengths and estimate the potential for soil-moisture measurements in the Argentinean Andes.</p>

Abstract. Cosmic-ray neutron sensing (CRNS) allows for the estimation of root-zone soil water content (SWC) at the scale of several hectares. In this paper, we present the data recorded by a dense CRNS network operated from 2019 to 2022 at an agricultural research site in Marquardt, Germany – the first multi-year CRNS cluster. Consisting, at its core, of eight permanently installed CRNS sensors, the cluster was supplemented by a wealth of complementary measurements: data from seven additional temporary CRNS sensors, partly collocated with the permanent ones, 27 SWC-profiles (mostly permanent), two groundwater observation wells, meteorological records, and global navigation satellite system reflectometry (GNSS-R). Complementary to these continuous measurements, numerous campaign-based activities provided data by mobile CRNS-roving, hyperspectral imagery via unmanned aerial systems (UAS), intensive manual sampling of soil properties (SWC, bulk density, organic matter, texture, soil hydraulic properties), and observations of biomass and snow (cover, depth, and density). The unique temporal coverage of three years entails a broad spectrum of hydro-meteorological conditions, including exceptional drought periods, extreme rainfall, but also episodes of snow coverage, as well as a dedicated irrigation experiment. Apart from serving to advance CRNS-related retrieval methods, this data set is expected to be useful for various disciplines, e.g. soil and groundwater hydrology, agriculture, or remote sensing. Hence, we show exemplary features of the data set in order to highlight the potential for such subsequent studies. The data is available at https://doi.org/10.23728/b2share.edfdaa0d2a82477fa512bde3f53312f2 (Heistermann et al., 2022b).

The combination of C-band and X-band radar networks has become increasingly popular in recent years, as it offers significant benefits for a range of applications. C-band and X-band radars use different frequencies, with the prior operating at around 5.6 GHz and the latter operating at around 9.3 GHz, leading to wavelengths of 5.3 and 3.2 cm, respectively. This means that the two types of radar have different characteristics and are suited to different applications. When combined, the two radar types complement each other's strengths and weaknesses. C-band radar can cover a larger area and provide a general overview of the environment being monitored, while X-band radar can provide detailed information about specific targets within that area. By combining these two types of radar, it is possible to obtain a more accurate and complete picture of the environment being monitored, with both high resolution and extended range. On the other hand, the combination of different-frequency radars in one processing chain brings several challenges. The backscattering profiles are different in each system, resulting in distinct observation patterns. Moreover, each frequency is subject to different attenuation rates, according to which, the appropriate corrections need to be applied. The German Weather Service (Deutscher Wetterdienst – DWD) operates a network of 17 C-band radars and in the following months will start to install four additional X-band systems in the urban areas of Karlsruhe, Nürnberg, Halle, and Bremen. The goal is to extend the coverage of the network and improve the early detection of thunderstorms that could potentially cause flash floods. As an initial step, we aim at quantifying the specific attenuation for all types of precipitation and the two frequencies. This process is fundamental for the realistic correction of the observations, particularly for higher-frequency signals that are more heavily impacted by attenuation.